Why the 'dig of the century' is happening underneath Notre Dame

France's famed Notre Dame cathedral has become the centre of an excavation dubbed by some as the "dig of the century". (Reuters: Tom Nicholson)

More than a year after France's famed Notre Dame reopened to the public, an archaeological exploration delving into thousands of years of the history of Paris and dubbed by some as the "dig of the century" has begun just metres below the cathedral's ground floor.

As the world watched on in 2019, a fire on Paris's Île de la Cité brought the cathedral's spire crashing down and sparked the beginning of a major process to rebuild and restore the medieval site.

The doors were thrown open once again in December 2024 at a lavish ceremony attended by French President Emmanuel Macron and more than 2,500 guests, such as then-US president-elect Donald Trump and Prince William.

Now Paris is seeking to continue the area's reformation by softening the hot, bare square located in front of Notre Dame with the addition of trees and shaded areas.

But in a city more than 2,000 years old, the soil cannot be turned until what lies beneath it is excavated, in case it is damaged during works.

So, a slice of Notre Dame's forecourt has become an excavation site — an open pit ringed by barriers and crossed by a wooden walkway, a few steps from the line-up.

Here is what excavators and archaeologists are hoping to find.

Excavators have already uncovered hundreds of historical artefacts. (AP: Nicolas Garriga)

Lucie Altenburg, a conservator with the Paris archaeology unit, told the Associated Press that the excavation underneath Notre Dame could develop the world's understanding of the city's past.

"It's a rare opportunity for us to work on something that's tangibly going to make a difference to the history of Paris," she said.

Excavators have already uncovered hundreds of historical artefacts, including a 4th-Century coin stamped with the face of the Emperor Constantine and shards of medieval pottery painted on the inside with marks no expert has yet deciphered — like a modern Da Vinci Code.

"It makes Notre Dame feel alive again," Emily Carter, a 34-year-old tourist from Manchester, said.

The first traces of Parisian history appear 50 centimetres under the surface of Notre Dame. Four metres lower than that, the archaeological team is still pulling up the past.

Some days they fill 15 crates with artefacts from the ground that has lain untouched for decades.

The bells of Notre Dame are chiming again, but scaffolding still clinging to the cathedral's exterior is puzzling some Parisians.

At the cathedral's birth in 1163, the enti